Braking energy recovery systems, also known as hybrid systems, have been known for a while in the field of electric vehicles such as cars and light trucks. In most of these applications, the energy recovered during braking, which would otherwise be dissipated as heat, is reused to drive the vehicle from a stop.
Refuse trucks are very well suited to the application of braking energy recovery systems. Indeed, the typical duty cycle of a refuse truck in collection mode is characterized by a high frequency of stop and go cycles and a low average speed. Furthermore, the energy consumption required by the frequent use of hydraulic auxiliary systems, such as the garbage compactor, is very high, reaching close to 40% in collection mode.
The “HRB Hydrostatic Regenerative Braking System™” from Rexroth, the “Runwise™” from Parker and the “Hydraulic Launch Assist™” from Eaton Corporation all use a combined hydraulic pump-motor. They are all designed for heavy truck applications where braking energy is recovered, stored and reused to launch the vehicle.
The Australian company Permo-Drive is active in the development of parallel hydraulic re-launch systems. Its product, named “Regenerative Drive Shaft” is a concentric pump/motor assembly placed around the vehicle's driveshaft that performs in pump mode to recover braking energy, and performs in motor mode to assist during acceleration from a stop.
Systems for assisting the vehicles during re-launch are however rather complex as they need to interface at different levels with the vehicle's drivetrain. Hence, an interesting alternative is to reuse the stored braking energy to power the auxiliary systems of vehicles making a large use of it, such as refuse trucks.
Different solutions have been proposed that recover the braking energy to power the auxiliary systems of a vehicle. United-States patent application no. US 2006/0108860 to Stragier describes a braking energy recovery system for refuse trucks that reuse the energy to power the auxiliary systems. However, the recovery system is not capable of adequately modulating the braking because its control acts basically as an ON/OFF switch.
United-States patent no. U.S. Pat. No. 4,778,020 to Hagin et al. describes a braking energy recovery system capable of storing braking energy in an accumulator to either drive a vehicle from a stop or to power its auxiliary systems. However, this recovery system requires the use of a complex variable transmission rather than a standard transmission, which limits the potential of use of this recovery system to retrofit existing vehicles.
There is therefore a clear need for an improved braking energy recovery system.